The present invention relates generally to invasive devices and methods for treatment of the heart, and specifically to devices and methods for pacing and electrical control of the heart muscle.
Modern cardiac pacemakers include not only pacing circuits, for generating pulses to pace the heart, but also sensing circuits, for sensing electrical activity in the heart tissue. Such pacemakers are designed to detect activation of the heart tissue due to sinus rhythm and generally to apply the pacing pulses only when appropriate intrinsic activation of the heart tissue does not occur.
U.S. Pat. No. 5,213,098, which is incorporated herein by reference, describes a pacing device that applies paired or triggered stimulation pulses in order to induce post-extrasystolic potentiation (PESP). The paired pulse is applied when the heart is paced, whereas the triggered pulse is applied when the heart is in sinus rhythm. The device is typically used to stimulate the right atrium in order to augment filling of the ventricles. One or more sensors are used to monitor physiological indicators of cardiac performance and stress. Signal processing circuitry varies a parameter of the stimulation, such as the frequency or number of heart cycles between periodic delivery of the pulses, dependent on the physiological indicators.
PCT patent application PCT/IL97/00012, published as WO 97/25098, to Ben-Haim et al., which is incorporated herein by reference, describes methods for modifying the force of contraction of at least a portion of a heart chamber by applying a non-excitatory electrical signal to the heart at a delay after electrical activation of the portion. In the context of the present patent application, the use of such a non-excitatory signal is referred to as Excitable Tissue Control (ETC). The non-excitatory signal may be applied in combination with a pacemaker or defibrillator, which applies an excitatory signal (i.e., pacing or defibrillation pulses) to the heart muscle.
It is an object of some aspects of the present invention to provide improved methods and apparatus for pacing of the heart together with Excitable Tissue Control (ETC) so as to modify or control hemodynamic performance of the heart under conditions of both paced and intrinsic cardiac rhythm.
In preferred embodiments of the present invention, an electrical cardiac stimulator comprises one or more pacing and/or sensing electrodes and one or more ETC electrodes, which are placed at respective sites in one or more chambers of the heart. An electrical control unit receives signals, preferably from the pacing and/or ETC electrodes, or alternatively, from dedicated sensing electrodes, indicative of electrical activation in the heart tissue. Responsive to the received signals, the control unit determines whether to pace the heart and, as appropriate, selects a suitable pacing mode and applies pacing pulses to the electrodes in accordance with the selected mode. The control unit sets parameters for ETC signals to be applied to the heart, dependent on whether the heart is paced and responsive to the selected pacing mode and pacing sites. The signals are applied to the ETC electrodes in accordance with the parameters, so as to provide optimal enhancement of contractility and reduced risk of arrhythmogenic effects of the ETC signals.
In some preferred embodiments of the present invention, the pacing and/or sensing electrodes are placed in the right atrium and right ventricle of the heart, and the ETC electrodes are placed in the left ventricle of the heart. The structure and function of the control unit and the placement of and signals applied to the electrodes are, preferably, generally as described in the above-mentioned U.S. Provisional Patent Application No. 60/107,479. The selection of ETC parameters is preferably dependent upon whether the heart is in sinus rhythm, or whether the heart is paced only in the right atrium, or in the right and/or left ventricle, as well. Further preferably, the ETC signals are applied responsive to a trigger, wherein the source of the trigger depends upon which site or sites are paced and from which sites the circuitry receives the signals indicative of tissue activation.
The parameters that are selected and varied by the circuitry preferably include timing parameters, particularly a duration of the ETC signals and a delay of the signals relative to the trigger. Selection of the timing parameters on this basis reflects differences in the propagation time and propagation paths of intrinsic electrical activation impulses in the heart as opposed to activation due to pacing. Alternatively or additionally, other signal parameters may be varied, including the voltage, current, duration, polarity, shape and frequency of the ETC signal waveform. Further alternatively or additionally, the duration and/or delay of the ETC signals is varied responsive to the heart rate, whether intrinsic or paced.
PCT patent application PCT/IL97/00236, and the corresponding U.S. patent application Ser. No. 09/254,900, which are assigned to the assignee of the present patent application and whose disclosures are incorporated herein by reference, also describe a pacemaker that gives cardiac output enhancement. This pacemaker applies both excitatory (pacing) and non-excitatory (ETC) electrical signals to the heart. By applying non-excitatory signals of suitable strength, appropriately timed with respect to the heart""s electrical activation, the contraction of selected segments of the heart muscle can be increased or decreased, thus increasing or decreasing the stroke volume of the heart.
There is therefore provided, in accordance with a preferred embodiment of the present invention, a method for modifying contractility of heart tissue, including:
applying electrodes to one or more sites in the heart;
making a determination at which of the sites, if any, to pace the heart;
setting a parameter of an excitable tissue control (ETC) signal to be applied to the heart responsive to the determination; and
applying the ETC signal to at least one of the electrodes responsive to the parameter, so as to enhance contractility of the heart.
Preferably, applying the ETC signal includes applying an electrical pulse, and setting the parameter includes setting a delay after which the pulse is to commence. Further preferably, setting the parameter includes assigning a trigger with respect to which the delay is set, wherein making the determination includes detecting electrical activity in the heart, and wherein assigning the trigger includes triggering responsive to the electrical activity.
Preferably, detecting the electrical activity includes detecting activity at or in a vicinity of the at least one of the electrodes to which the ETC signal is applied. Alternatively or additionally, detecting the electrical activity includes detecting activity in the left ventricle of the heart while the heart is paced at one of the electrodes in another chamber of the heart. Further preferably, triggering responsive to the electrical activity includes sensing electrical activation of the tissue and triggering thereon.
In a preferred embodiment, the method includes applying pacing pulses to the heart in accordance with the determination, wherein assigning the trigger includes triggering on one of the pacing pulses. Preferably, triggering on the one of the pacing pulses includes triggering on a pacing pulse applied to the at least one of the electrodes to which the ETC signal is applied. Alternatively or additionally, triggering on the one of the pacing pulses includes triggering on a pacing pulse applied in the left ventricle of the heart.
Preferably, setting the delay includes setting a delay responsive to the determination so as to substantially eliminate the possibility that a new action potential will propagate in the heart tissue responsive to the ETC signal. Additionally or alternatively, setting the delay comprises setting a variable delay responsive to a beat rate of the heart.
Preferably, applying the ETC signal includes applying an electrical waveform, and setting the parameter includes setting a duration of the waveform, wherein setting the duration includes selecting a waveform type and setting the duration responsive to the type. Further preferably, setting the duration includes setting a duration responsive to the determination so as to substantially eliminate the possibility that a new action potential will propagate in the heart tissue responsive to the ETC signal.
Preferably, applying the electrodes includes applying electrodes in two or more chambers of the heart.
There is also provided, in accordance with a preferred embodiment of the present invention, apparatus for modifying contractility of heart tissue, including:
one or more electrodes, which are applied at respective sites in the heart, and
an electrical control unit, which makes a determination at which of the sites, if any, to pace the heart, and which sets a parameter of an excitable tissue control (ETC) signal to be applied to the heart responsive to the determination and applies the ETC signal to at least one of the electrodes responsive to the parameter, so as to enhance contractility of the heart.
Preferably, the ETC signal includes an electrical pulse, and the parameter set by the control unit includes a delay after which the pulse is to commence. Further preferably, the control unit sets a trigger with respect to which the delay is set, wherein the control unit receives signals from at least one of the electrodes responsive to electrical activity in the heart and sets the trigger based on the electrical activity.
Preferably, the control unit receives the signals from the at least one of the electrodes to which it applies the ETC signal. Alternatively or additionally, the control unit receives the signals from one of the electrodes in the left ventricle of the heart while the heart is paced at another one of the electrodes in another chamber of the heart. Preferably, the control unit senses electrical activation of the tissue and sets the trigger at the time of activation.
In a preferred embodiment, the control unit applies pacing pulses to the heart in accordance with the determination and sets the trigger on one of the pacing pulses. Preferably, the control unit sets the trigger on a pacing pulse applied to the at least one of the electrodes to which the ETC signal is applied. Alternatively or additionally, the control unit sets the trigger on a pacing pulse applied in the left ventricle of the heart.
Preferably, the control unit sets the delay so as to substantially eliminate the possibility that a new action potential will propagate in the heart tissue responsive to the ETC signal. Additionally or alternatively, the control unit varies the delay responsive to a beat rate of the heart.
Further preferably, the ETC signal applied by the control unit includes an electrical waveform, and wherein the parameter set by the control unit includes a duration of the waveform, wherein the control unit selects a waveform type and sets the duration responsive to the type. Preferably, the control unit sets the duration responsive to the determination so as to substantially eliminate the possibility that a new action potential will propagate in the heart tissue responsive to the ETC signal.
Preferably, the electrodes are applied in two or more chambers of the heart.